When diagnosing and treating various bodily ailments, such as with patients suffering from shock or cardiovascular problems, medical personnel often find it desirable to measure and/or monitor a patient's blood pressure. Advantageously, by measuring and/or monitoring the blood pressure of these and other types of patients, medical personnel are better able to detect blood flow difficulties and other cardiovascular problems at an early stage. As a result, the use of blood pressure measurement and monitoring may increase the likelihood that a patient can be successfully treated and/or provided with needed emergency assistance.
A variety of methods are currently used for measuring and/or monitoring blood pressure. For example, medical personnel frequently use various indirect blood pressure measurement techniques, such as measuring a patient's blood pressure by using a pressure cuff and a stethoscope. In addition, blood pressure measurements are often made using a number of direct measurement and monitoring techniques. Notably, when diagnosing and/or treating critically ill patients, such direct techniques are greatly preferred over any of the indirect techniques. Direct blood pressure measurement and monitoring techniques are generally accurate to within about one percent, and facilitate the continuous monitoring of a patient's blood pressure on a beat-to-beat basis. Direct blood pressure monitoring also enables the rapid detection of a change in cardiovascular activity, and this may be of significant importance in emergency situations.
In direct, or invasive, blood pressure monitoring systems a catheter is inserted into a patient's circulatory system with the end of the catheter having an opening to the blood stream, typically in a major or peripheral blood vessel. First, a needle is inserted into a peripheral blood vessel. For example, if it is desired to monitor arterial blood pressure, the needle may be inserted into the radial artery. If, on the other hand, venous blood pressure is to be monitored, the needle may be inserted into the antecubital, radial, jugular, or subclavian veins. Once the needle is properly inserted, a special catheter is threaded through the needle and into the blood vessel until the tip of the catheter is positioned at the particular point within the body at which it is desired to make the blood pressure measurement. Then, with the catheter in place, the needle may be withdrawn.
An I.V. set attaches to the proximal end of the catheter protruding from the patient so that a solution flows through the catheter and into the patient. The I.V. solution provides a fluid “column” through which pressure pulses are transmitted, and a pressure transducer positioned along the fluid column monitors those pressure pulses. Generally, the pressure transducer consists of a dome that functions as a reservoir for the I.V. fluid. The dome includes a resilient diaphragm that attaches to an electrical transducer. The transducer senses pressure fluctuations in the diaphragm and converts them into electrical signals which then transmit through a cable to a monitor for amplification and display. In modern systems a single silicon chip comprises both the pressure diaphragm and the measuring circuitry of the pressure transducer. Since such silicon chips are cheaply mass-produced, the total cost of pressure transducers is reduced to the extent that the transducer becomes economically disposable. The cable includes a connector so that the transducer and associated portion of the cable can be discarded after use, whereas the mating connector and cable hard-wired to the monitor can be reused. Such disposable blood pressure transducers (DPTs) are the standard of care in the OR, ICU or CCU.
Due to the separable nature of the transducer and monitor, different transducers may be connected to any one monitor, as long as the cable connectors are compatible. However, transducers from different sources may exhibit different performance characteristics and may require specific calibration and/or signal processing or conditioning. Unfortunately, the environments of the OR, ICU or CCU are ill-suited for rapid recognition and registration of disparate components of pressure monitoring systems, and safety concerns necessitate the least amount of such preparation be involved.
Furthermore, pressure data are often required by two separate monitoring devices, such as a patient monitor and a cardiac output monitor, or a patient monitor and an aortic balloon pump. Typically, an arterial line is placed in the patient and a DPT connected to a patient monitor is used for pressure monitoring. Instead of invasively setting up a second arterial line and DPT, the signal from the first DPT may be supplied to a second monitor via the patient monitor. However, this “piggyback” connection may introduce pressure monitoring errors from delays and distortion of the signals.
Despite a relatively mature market for disposable medical pressure transducers, there remains a need for a “smart” transducer that when interfaced with the appropriate monitoring device ensures accuracy. There is also a need for a simpler and more reliable system for transmitting the pressure signal to multiple instruments.